Method of eliminating cross talk in phantomed transmission systems



June 12, 1928.

H. KARSTEN ET AL METHOD OF ELIMINATING cnoss TALK IN PHANTOMEDTRANSMISSION SYSTEMS Filed July 15, 1926 ffiws KARSTE/v g ifm Kym/011m AORNEY Patented June 12, 3928.

warren STATEs HANS masmnn, or nnnnm-onannor'rnnnune, AND KARLKfi'PFll/IfiLLER, or BER- LIN-FBIEDENAU, GERMANY, ASSIGNOBS T SIEMENS &HALSKE AKTIENGESELL- SCHAFT, A GERMAN COMPANY.

METHOD or ELIMINATING craoss TALK IN PHANTOMED TRANSMISSION SYSTEMS.

Application filed July 15, 1926, Serial No. 122,742, and in Germany July18, 1925.

This invention relates to phantomed transmission systems andparticularly to methods for reducing cross-talk within and betweenadjacent phantomed lines.

Cross-talk in multiple telephone cables occurs principally bet-weenspecially connected speaking circuits. These are the speaking circuitsbelonging to a quad, i. e., the phantom circuit and the two sidecircuitsand 19 also the speaking circuits of two quads placed near toeach other in the cross-section of the cable. Methods for balancing outthe crosstalk between the speaking circuits of" a quadded cable and alsobetween the phantom circuits of two quads are well known. On the otherhand no method has been known heretofore, for balancing the crosstalkbetween all the speaking circuits of two cable quads. Experience hasproved it to be a necessity, however, to extend the balancing of thecross-talk to all the speaking circuits of two mutually related cablequads. This invention relates to the solution of this problem.

The invention is based upon the well known fact that cross-talk betweentwo cable lines is mainly due to the presence of capacity couplings, theelimination of which, by inserting suitably proportioned condensersbetween particular wires of the inducing lines, is theoreticallypossible. Between the three speaking circuits of each of two cable quadsthere are nine couplings, viz., one coupling between the two phantomcircuits, four couplings between the phantom and side circuits, and fourcouplings between the side circuits. These three kinds of couplings,phantom to phantom, phantom to side, and side to side, are dependent oneach other so that generally in varying a coupling, for example bybalancing the same by means of additional condensers, each coupling ofthe other kinds is also varied in its original magnitude. Similarly, thecross-talk couplings within a single phantomed circuit or quad aredependent upon the couplings of the circuits of that quad with thecircuits of neighbouring quads. A direct capacity balance is thus notpossible.

Broadly this invention consists in balance ing the individual speakingcircuits in such manner that the balancing arran ements act as far aspossible independent y of each other, or so that they influence eachother in such a manner as to simplif vthe process.

According to a feature 0 this invention the couplings between thespeaking circuits of neighbouring quads are first balanced and then thecouplings within each quad are balanced. As the balancing of thecross-talk couplin effects within a phantomed circuit afiects te balanceof the cross-talk between the speaking circuits of the adjacentphantomed circuits, those changes in the couplings within the phantomedcircuit, which have been caused by the previous balancing of thecouplings between the circuits of the ad acent phantomed circuits, canbe taken nto account at the time the couplings within a circuit arebalanced. If, on the other hand, the succession were reversed, thebalancmg within the quad would be again disturbed by balancing thecross-talk between the circuits of adjoining quads.

According to another feature of this invention, a certain order ofprocedure is adhered to in balancing the couplin s between the circuitsof the adjacent qua s, namely the couplings between the phantom circuitsare balanced after the side to side and phantom to side couplings havebeen balanced. If, when balancing the phantom to phantom couplingsquadruple condensers, such as are described in German Patent No.396,634, are used, the phantom to phantom balance may be made withoutany influence on the phantom to side and side to side balance.

Moreover, it is necessary to balance the phantom to side couplings andthe side to side couplin s independently of each other. This can be onein the following manner As is well known, the couplings are composed ofthe sums and differences of the component capacities between theindividual wires, so that mutually dependent couplings contain the samecomponent capacities in common. Thus each phantom to side couplingcontains the sum or the diiierence of two component capacities whichconversely appear as a difference or a sum in one and only one side toside coupling. Therefore, if, when balancing, for example a phantom toside coupling, the inserted capacity value is divided into two equalparts each of which is placed in parallel with one of the two componentcapacities, thus ice adding together in their efiect' on the couplin .sbeing balanced, then all side to side coup%ings, even those containingthese component capacities, maintain their or ginal ma itudes. This isdue to the fact that the variation of one component capacity isneutralized b a variation of similar ma nitude of the ot er componentcapacity w ich is connected, in this case, in an opposite manner. Thebalance of phantom to side and side to side couplings must thus be madein such a manner that each coupling is balanced by two equal condenserswhich are connected to the wires of the cable in such a way that thecomponent capacities, which add together in pairs in their effect on thecoupling, are in parallel.

In balancing the phantom to side couplings there are two ways ofinserting the condensers, one having a positive and the other a negativeeffect on the phantom to phantom coupling. It is advantageous to soinsert the condensers that simultaneously 7 with the balancing of thephantom to side coupling the amount of the phantom to phantom couplingis reduced. Thus, the use of a special condenser for phantom to phantombalancing may be avoided, if, by doing this, the phantom to phantom couling is reduced to the tolerance value or at east the value of thecondenser required for the phantom to phantom balance is reduced. Thepractical accomplishing of cross-talk balancing between the speakingcircuits of different phantomed circuits can be done as follows Y Thetwo cable quads are connected through a rheostat to a coupling meter bymeans of special leads. By varying the switch positions the cable wirescan be connected in nine combinations to the coupling meter and in thevarious switch positions the following couplings can be measured PhantomI to phantom II, side 1 of the quad I to phantom II, side 2 of the quadI to phantom II, phantom I to side 1 of the quad II, phantom I to side 2of the quad II, side 1 of the quad I to side 1 of the quad II, side 2 ofthe quad I to side 1 of the quad II, side 1 of the quad I to side 2 ofthe quad II, side 2 of the quad I to side 2 of the quad II. The methodof the invention for reducing cross-talk couplings within and betweenadjacent phantomed lines will be clear by inspection of the accompanyingdrawing, Fig. 1 of which shows schematically the crosstalk couplingsexisting between the various speaking circuits of two phantomed quads ina multiple telephone cable and Fig. 2 of which is a table indicating thepreferable order of procedure in accordance with the invention forbalancing out these cross-talk couplings.

Referring to Fig, 1 of the drawing, two adjacent quads Q, and Q, areshown, the

quad Q comprising side circuits. S and S, and phantom circuit P and thequad Q, comprising side circuits S and S, and phantom circuit P Thecross-talkcouplings between the circuits of the adjacent quads andbetween the circuits within the quads are indicated by the arrowsextending between the various circuits. As indicated in the tableof Fig.2, the order of balancing the cross-talk couplings is first, to balancethe coupling between the speaking circuits of the adjacent quads, i. e.the side to side and side to phantom couplings in any desired order,secondly, to balance the coupling between the phantom circuits of theadjacent quads, and thirdly, to balance the couplings within each quadin any desired order.

The determination of the cable wires to which the various balancingcondensers are to be connected can be facilitated by using a tabulatedrecord. The number of the coupllngs to be balanced would of course bearge if it were not limited for practical reasons to only the couplingsbetween the speaking circuits of those quads which need to be balancedbecause they lie close together and parallel to each other in thecross-section of the cable, and further by the fact that a certaintolerance in the accuracy of balancing is allowable.

What is claimed is:

1. The method of eliminating cross-talk between the speaking circuits ofdifferent phantomed lines or quads by means of condensers, characterizedin this that first the cross-talk couplings between the circuits ofadjacent quads are balanced and then the cross-talk couplings withineach quad are balanced.

2. A method in accordance with claim 1, characterized in this that inbalancing the cross-talk between circuits of the different quads theside to side and phantom to side couplings are first balanced and thenthe phantom to phantom couplings are balanced.

3. A method in accordance with claim 1 characterized in this that eachcoupling for the phantom to side and side to side crosstalk is balancedby two condensers of half the coupling capacity, said condensers beingconnected in parallel to the two component capacities so as to addtogether in their elfect on the coupling which has to be balanced.

4. A method in accordance with claim 1 characterized in this that suchpartial capacities are used for balancing the phantom to side couplingsthat at the same time the phantom to-phantom coupling is reduced.

In witness whereof, we hereunto subscribe our names this 2nd day ofJuly, A. D. 1926.

HANS KABSTEN. I KARL KUPFMIlLLER.

